Contents - Previous - Next


This is the old United Nations University website. Visit the new site at http://unu.edu


Protein-Energy Requirements Data Sought

The Food and Agriculture Organization, the World Health Organization, and the United Nations University will hold an expert committee meeting on protein energy requirements in October 1981. For the guidance of committee members, the following data on child growth are needed urgently:

- Data on variations in normal growth within short periods, i.e., daily, weekly, bi-weekly, or even monthly. In particular, data on individual children are sought.

- Data from longitudinal studies relating growth to diet with special reference to dietary protein versus energy.

- Data on the age at which growth stops in various populations; i.e., do disadvantaged populations show any compensation by extending the normal growth period?

Individuals with relevant data are urged to communicate directly with Dr. Julien Prisse, Food Policy and Nutrition Division, Food and Agriculture Organization, Via delle Terme di Caracalla, 00100 Rome, Italy.

The calorie densities of gruels made from extruded corn-soy blends

G.R. Jansen, L. O'Deen, R.E. Tribelhorn, and J. M. Harper

Departments of Food Science and Nutrition and Agricultural and Chemical Engineering, Colorado State University, Fort Collins, Colorado, USA

Supplemental foods based on blends of corn, soybeans, and in most cases non-fat dry milk fortified with vitamins and minerals have been distributed since September 1966 through the Food for Peace Program (1,2). These foods are high in protein, vitamins, and minerals, and are able to improve the diet of the recipient child both quantitatively (calories) and qualitatively (nutrient density).

Because breast milk becomes inadequate as the sole source of food by four to six months and even earlier in some under-privileged populations, Waterlow (3) and others (4) have stressed the importance of supplementary feeding for infants and mothers. Since the amount of a cereal gruel that an infant can eat is often limited by its volume, the calorie and nutrient density of the gruel as actually consumed becomes an important consideration.

Calorie density is generally thought of in terms of the levels of fat, carbohydrate, protein, and fibre in a food product. However, in the case of cereal gruels, viscosity would appear to be a more important determinant. The viscosity of these gruels, in turn depends in large part on the degree of starch gelatinization. Extrusion technology has been widely used in manufacturing blended foods for use in supplemental feeding programmes (5,6). The effect of extrusion on starch gelatinization and the viscosity of gruels made from these blends has been evaluated by a number of investigators (5-9). However, the effect of extrusion on the calorie densities of gruels made from cereal blends does not appear to have been examined.

In the work to be described in this paper, the effect of extrusion on the calorie density of corn-soy blend gruels was investigated. Comparisons are made between corn-soy milk (CSM) and instant corn-soy milk (ICSM) as made commercially and distributed in the US Food for Peace Program. A dry or "autogenous" extrusion process was used with little added moisture and no added heat other than that from the frictional dissipation of the mechanical power input. The Brady extruder used is such an extruder, referred to as a low-cost extruder cooker (LEC), which is being used to make weaning foods in a number of developing countries (10).

METHODS

Sample preparation. Corn and soybeans were dehulled using a Sturtivant scourer-aspirator. Corn-soy blends (CSB) made from 70 parts corn and 30 parts soy were proportioned and coarsely ground in a Modern mill model 600. A Brady model 216 extruded samples at 149C or 171C, with water metered in during extrusion at 86 ml/min and a dry feed rate of 5.6 kg/min. The raw ingredient averaged approximately 10 per cent moisture, which was reduced to 4 to 5 per cent after extrusion. The proximate composition of the CSB was in percentage dry weight: 8.87 0.42 per cent fat; 1.51 0.08 per cent crude fibre; 2.71 0.03 per cent ash; 20.1 0.1 per cent protein (N x 6.25), and 66.8 0.6 per cent carbohydrate CSB was also extruded at 149C and 171C after pre-conditioning by adding 9 per cent water in a blender and allowing it to stand for three hours prior to extrusion. Dehulled corn alone (6.6 kg/min) was also extruded at 149C or 171C with water metered in at the rate of 120 ml/min during extrusion. All samples were ground twice on a Fitz mill, first using an 0.127 cm screen and then an 0.0686 cm screen. In some cases, soy oil, sugar, non-fat dry milk (NFDM), or an amylase Phozyme H39 (Rohm and Haas) were added to the CSB after grinding, using a Hobart mixer, at the levels listed in tables 1 and 2.

Title II corn-soy milk (CSM) and instant corn-soy milk (ICSM) were obtained from the Krause Milling Company, Milwaukee, Wisconsin, USA. The formulation for CSM is for 62 per cent partially gelatinized, degerminated cornmeal, 18 per cent defatted toasted soy flour, 5 per cent oil, and 15 per cent non-fat dry milk fortified with vitamins and minerals (11). The formulation for ICSM is for 15 per cent fully gelatinized, degerminated cornmeal, 30 per cent full-fat soy flour, and 5 per cent non-fat dry milk fortified with vitamins and minerals (12). Title II CSB was unavailable, but this commodity is made from 72 per cent partially gelatinized, degerminated cornmeal, 23 per cent defatted, toasted soy flour, and 5 per cent oil fortified with vitamins and minerals.

Preparation of gruels. Gruels were made using either an "instant" or a "cooking" procedure. In the "instant" procedure, the samples were weighed and stirred into 100 ml of water at 70C. The lumps were mashed, and the viscosity was measured at 45C to 50C using a Brookfield viscometer at 50 rpm and a number 5 spindle. In the "Cooking" procedure, a small quantity of cold water was added to make a smooth paste, followed by the addition of boiling water. The gruel was then boiled for 10 minutes, cooled to 50C, made back up to volume, and the viscosity measured as described above.

Determination of calorie density. Gruels were made from Gerber's Mixed Cereal according to package instructions, but using water instead of milk. The viscosity of this gruel at a consistency judged suitable for feeding an infant was 1,600 cps when measured at 45C to 50C using a Brookfield viscometer at 50 rpm with a number 5 spindle, Plots of viscosity (cps) versus concentration (grams cereal sample per 100 g mixture) were used to establish the concentration of sample that would produce the reference viscosity of 1,600 cps. Four to six concentrations were plotted for each sample to establish the concentration-viscosity relationships. Calorie densities in kilocalories per 100 ml were calculated from these concentrations, proximate analysis, and density data using 4 kcal/g for protein and carbohydrate, and 9 kcal/g for fat.

RESULTS

Viscosity-concentration curves for "instant" and "cooked" gruels made from dehulled raw or extruded (149C) corn are shown in figure 1. Since raw corn is completely ungelatinized, it resulted in an "instant" gruel with very low viscosity even at high concentrations. However, when "cooked," the raw corn gelatinized rapidly, producing very high viscosity. The extruded corn produced intermediate viscosity concentration curves that were very similar using either the "instant" or the "cooking" preparation procedure.

Fig. 1. Viscosity-Concentration Curves for Gruels Made from Raw Corn or from Corn Extruded at 149C, Using Either the "Instant" or the "Cooking" Procedure

Fig. 2. Viscosity-Concentration Curves for Gruels Made Using the "Instant" Procedure from CSB Extruded at 149C (LEC-CSB); LEC-CSB with 15 Per Cent NFDM Added (LEC-CSM): Title II CSM; Title II ICSM; and LEC-CSB with 0.010 Per Cent Rhozyme H39 (LEC-CSB-ENZ)

Fig 3. Viscosity-Concentration Curves for Gruels Made Using the "Cooking" Procedure from CSB Extruded at 149C (LEC-CSB); LEC-CSB with 15 Per Cent NFDM Added (LEC-CSM); and Raw CSB

In figure 2, viscosity concentration curves for "instant" gruels made from extruded CSB (LEC-CSB), CSM (LEC-CSM), and enzyme-treated extruded CSB (LEC-CSB-ENZ) are compared with the corresponding curves for Title II CSM and ICSM. The LEC-CSB sample exhibited a viscosity curve similar to that for ICSM, suggesting that the starch in the LEC extrusion is, in effect, gelatinized. Adding non-fat dry milk (NFDM) shifts the viscosity curve to the right, since NFDM does not contain starch and produces little viscosity. The Title II CSM contains only partly gelatinized starch (11) and, therefore, little viscosity is produced except at higher concentrations. The enzyme-treated LEC CSB resulted in a viscosity-concentration curve similar to that observed for CSM.

In figure 3, viscosity concentration curves for "cooked" gruels made from LEC-CSB, LEC-CSM, and raw CSB are compared. As was the case for raw corn, the raw CSB gelatinized rapidly when cooked, producing higher viscosities at much lower concentrations than was the case for the extruded LEC CSB. Addition of NFDM to the CSB (LEC-CSM) moved the curve to the right, although the magnitude of the shift was slightly smaller than observed for the "instant" gruels.

The calorie densities for "instant" and "cooked" gruels made from corn, CSB, CSM, and ICSM are presented in table 1. Using the "instant" gruel procedure, raw CSB or raw corn produced gruels with the very high caloric densities of 153.7 and 149.4 kcal/100 me respectively. These gruels would, however, be unacceptable because of their completely uncooked nature. LEC-CSB extruded at 149C and 171C resulted in caloric densities of 84.4 and 76.0 kcal/100 ml, respectively. Addition of 15 per cent NFDM raised these values to 91.6 and 84.6 kcal/100 ml respectively, values closely similar to the value of 84.1 kcal/100 ml observed for Title II ICSM. The calorie density for the "instant" gruel made from Title II CSM was about halfway between the values for raw CSB and ICSM and consistent with the fact that the corn in this product is only partially gelatinized, Calorie densities for the gruels made from LEC-extruded corn were similar to the value for the gruel made from the commercial mixed cereal, again supportive of the contention that the LEC process is capable of producing "instant" cereal products.

Corresponding data for "cooked" gruels are also shown in table 1. Extruding CSB at 149C resulted in calorie densities for cooked gruels of 64.5 and 75.2 kcal/100 ml, respectively, compared to only 43.3 kcal/100 ml for raw CSB. Addition of 15 per cent NFDM increased the calorie densities to 77.9 and 84.8 kcal/100 ml for CSB extruded at 149C and 171C, respectively. The calorie densities for cooked gruels made from Title II CSM and ICSM were 56,1 and 51.0 kcal/100 ml, respectively. These values are higher than that for raw CSB, but considerably lower than the values observed for LEC-CSBs.

TABLE 1. Effect of Extrusion on Calorie Densities of Cereal Gruels of Uniform Consistency

Sample "Instant" gruel "Cooked" gruel
g cereal product/100 ml kcal/100 ml g cereal product/100 ml kcal/100 ml
CSB, raw 39.5 153.7 11.1 43.3
CSB, extruded 149C 20.9 84.4 16.0 64.5
CSB extruded 149C        
+15% NFDM* 23.5 91.6 20.0 77.9
CSB, extruded 171C 18.7 76.0 18.5 75.2
CBS, extruded 171C +15% NFDM* 21.7 84.6 21.8 84.8
Title II CSM 32.0 121.6 14.8 56.1
Title II ICSM 22.1 84.1 13.4 51.0
Corn, raw 40.7 149.4 8.3 30.3
Corn, extruded 149C 16.3 62.2 15.9 60.6
Corn, extruded 171C 15.8 61.2 16.3 63.0
Gerber's Mixed Cereal 16.8 62.5 15.9 59.1


* Percentage of the final weight of the blend.

TABLE 2. Effect of Pre-conditioning, Enzyme Treatment, Oil, or Sugar Addition on Calorie Density of Gruels of Uniform Consistency

Sample "Instant" gruel   "Cooked" gruel  
  g cereal product/100 ml kcal/100 ml g cereal product/100 ml kcal/100 ml
CSB, extruded 149C 20.9 84.4 16.0 64.5
CSB, extruded 149C, pre-conditioned* 19.1 73.9 19.6 76.0
CSB extruded 149C +4% soy oil2 20.0 84.4 18.0 76.2
CSB, extruded 149C+10% sugar 21.5 86.1 18.2 72.9
CSB, extruded 149C +0.010% enzyme** 30.6 123.6 19.8 80.1
CSB, extruded 171C 18.7 76.0 18.5 75.2
CSB, extruded 171C pre-conditioned* 19.7 75.5 20.2 77.2
CSB extruded 171C+4% Soy Oil 19.9 84.9 19.3 82.2
CSB Extruded 171C+10% Sugar 20.4 82.9 21.5 87.3

* Pre-conditioned with g per cent water for three hours prior to extrusion.
** Percentages of the final weight of the blends. Rhozyme H39 obtained from Rohm and Hess Company, Philadelphia, Penn., USA.

Effects of pre-conditioning with water before extrusion, or addition, after extrusion, of oil, sugar, or enzyme to LEC-CSB on the caloric densities of "instant" and "cooked" gruels made from these blends are summarized in table 2. Pre conditioning ingredients with 9 per cent water for three hours before extrusion had little effect on calorie density except for cooked gruels made using LEC-CSB extruded at 149C, where water addition increased calorie density from 64.5 to 76.0 kcal/100 ml. Addition of oft or sugar generally increased the calorie densities of the "instant" or "cooked" gruel s at both extrusion temperatures, although the increases were relatively modest. Addition of as little as 0.01 per cent of the Rhozyme H39 increased the calorie density of the uncooked gruel made from LEC-CSB from 84.4 to 123.6 kcal/100 ml - a 46 per cent increase. Using the cooking procedure for making gruels, the enzyme treatment increased calorie density by 24 per cent.

DISCUSSION

Calorie densities of cereal gruels can be compared only in relation to an arbitrary consistency. In this study, the reference point was a cereal gruel made from a commercial, pre-cooked baby cereal that was judged by experienced mothers to be at the right degree of thickness for feeding to infants by spoon. This gruel was made by adding 5.6 parts by weight of water to one part of cereal. In a survey of infant feeding practices in lows, USA, Anderson and Fomon (13) found that, in feeding infants 5 to 14 months of age, 5.5 parts of milk were used per Part of cereal. Therefore, the reference point used for calorie density comparisons in this study would appear to be a reasonable one.

For reasons of sanitation, water used in making gruels to be used as weaning foods in developing countries should be bolted for 10 to 15 minutes. In some cases, the water is boiled before mixing with the cereal, and in other cases, the gruel is cooked for 10 minutes. In either case, the LEC process would appear to be advantageous in making weaning foods to be used as gruels in feeding programmer. LEC-CSB, as manufactured by this dry extrusion process, can be considered a pre-cooked or "instant" cereal product that can be made into a gruel by mixing with previously bolted water. This has the advantage of saving fuel because water is normally bolted in a large container. On the other hand, if the gruel is "cooked" for up to 10 minutes, the extruded product results in a gruel with substantially increased calorie density compared to a raw cereal product. At a given volume of intake by a child, the extruded cereal product would also substantially increase protein intake, and, if the weaning food were fortified with vitamins and minerals, micro-nutrients as well.

To the extent possible, the addition of sugar and NFDM to the LEC-CSB is desirable, essentially converting this product into LEC-ICSM. Both sugar and NFDM increased the calorie densities of the gruels, and experience suggests that both are helpful in increasing the acceptability of cereal gruels. From a nutritional standpoint, however, the LEC-CSB, even without the added milk, has been demonstrated to contain protein of excellent quality, comparable to casein, in metabolic studies carried out in human infants (14).

The addition of a small amount of amylase to the dry blend would appear advantageous as far as calorie density is concerned, if such enzyme addition is allowable under the food laws in the country of application. The Codex Alimentarius (15) allows enzyme use in infant cereals conforming to "... good manufacturing practice." The level of addition would have to be carefully controlled. Use of too high an amylase level would liquify the gruel and potentially encourage bottle-feeding and discourage breast-feeding. This would be contrary to current WHO policy on infant feeding practices (16).

It is of interest that a high degree of apparent starch gelatinization and pre-cooking occurred in this low-moisture extrusion process. The results, however, are consistent with the work of Lawton et al. (17), who reported that in extrusion, the maximum degree of gelatinization occurred at high moisture-low temperature or low moisture-high temperature. However, in their experiments, the lowest moisture level used was 27 per cent, high enough to satisfy the theoretical requirements for bound water in the gelatinization process. In the LEC process, less water is used, below the amounts needed for normal gelatinization. It appears that in this dry extrusion process, a combination of heat and shear disrupts the starch granules, unfolds, and breaks the starch chains, resulting in a product that hydrates quickly with water without additional cooking and is readily hydrolyzed by enzymes.

The LEC process is of potential advantage in processing cereal grains intended for use as baby cereals even without the addition of oilseeds or legumes. Processing costs are estimated to be five cents per kilogram. Since there seems to be a general feeling that consumption of cereals by infants and pre-school age children in developing countries is often limited by the volume that can be consumed, the doubling of the calorie density of the cooked cereal gruel may well be worth the processing cost. In addition, the added shelf life due to "pasteurization" by the high temperature-short time extrusion process while the cereal is pre-cooked, means less use of home cooking fuels, both of which are advantages, even for a cereal alone.

SUMMARY

The calorie densities of gruels made from raw or extruded corn-soy blends (CSB) were measured. Extrusion was carried out under low-moisture conditions using a Brady extruder, referred to as a low-cost extruder cooker (LEC). The effects of sugar, oil, non-fat dry milk, or amylase addition were evaluated, and comparisons were made with Title II corn-soy milk (CSM) and instant corn-soy milk (ICSM). Gruels were made both by the "instant" procedure, in which the product was mixed with previously boiled water, or a "cooking" procedure where they were boiled together for 10 minutes.

CSB made using the LEC process (LEC-CSB) produced "instant" gruels comparable in viscosity and calorie density properties to ICSM and, therefore, can be considered a pre-cooked cereal product. Using the cooking procedure for making gruels, the LEC-CSB resulted in gruels substantially higher in calorie density than gruels made from raw CSB. A further increase in calorie density resulted from the addition of sugar, oil, or dry milk. The addition of as little as 0.10 per cent of a bacterial amylase to the dry LEC-CSB greatly increased calorie density.

It was concluded that the LEC process produces precooked, blended foods that have advantages as weaning foods used in feeding programmer, whether gruels made from these products are used with or without additional cooking. It is suggested that the LEC process might also be advantageous in making pre-cooked cereals intended for use as infant cereals, even if no oilseeds or legumes are added.

REFERENCES

1. R. A. Anderson, V. F. Pfeifer, G. N. Bookwalter, and E. L. Griffin, Jr., "Instant CSM Food Blends for World-Wide Feeding," Cereal Sci. Today, 16 (1): 5-11 (1971).

2. F. R. Sente, "Soy Protein Foods in U.S. Assistance Programs," J. Am. Oil Chem. Soc., 51: 138A (1974).

3. J. C. Waterlow, "Observations on the Protein and Energy Requirements of Pre-school Children," Indian J. Nutr. Dietet., 16: 175-188 (1979).

4. N. S. Scrimshaw and B. A. Underwood, "Timely and Appropriate Complementary Feeding of the Breast-fed Infant - An Overview," Food and Nutrition Bulletin, 2 (2): 19-22 (1980).

5. J. M. Harper, "Food Extrusion," CRC Critical Reviews in Food Science and Nutrition, 11: 155-215(1979).

6. O. B. Smith, "Extrusion Cooking," in A. M. Altschul, ed., New Protein Foods, vol. 2B (Academic Press, New York, 1976), p.86.

7. H. F. Conway, "Extrusion Cooking of Cereals and Soybeans," part I, Food Prod. Dev., 5 (2): 27-29 (1971).

8. H. F. Conway, "Extrusion Cooking of Cereals and Soybeans," part II, Food Prod. Dev., 5 (3): 14-17 (1971).

9. G. N. Bookwalter, A. J. Peolinski, and V. F. Pfeifer, "Using a Bostwick Consistometer to Measure Consistencies of Processed Corn Meals and Their CSM Blends," Cereal Sci. Today, 13 (11): 407-410 (1968).

10. G. R. Jansen, and J. M. Harper, "Applications of Low-Cost Extrusion Cooking to Weaning Foods in Feeding Programs," FAO Food and Nutrition (in press).

11. "Purchase of Corn-Soya Milk for Use in Export Programs," Corn-Soy Milk Announcement CSM-7, issued 25 July 1975, with subsequent amendments (USDA/ASCS Commodity Office, Shawnee Mission, Kans., USA).

12. Instant Corn-Soya Milk Export Announcement CSM-5, issued 25 July 1975, with subsequent amendments (USDA/ASCS Commodity Office, Shawnee Mission, Kans., USA).

13. T. A. Anderson and S. J. Fomon, "Commercially Prepared Infant Cereals: Nutritional Considerations," J. Pediat, 78: 788-793 (1971).

14. G. G. Graham and W. L. McLean, Jr. "Digestibility and Utilization of Extrusion-Cooked Corn-Soy Blends," report submitted to the office of nutrition, Agency for International Development (Washington, D.C., 1979).

15. Codex Alimentarius Commission, "Recommended International Standards for Foods for Infants and Children," CAC/RS 72/74-1976 (Food and Agriculture Organization, Rome, 1976).

16. "Statement on Infant and Young Child Feeding" (World Health Organization, Geneva, 1979).

17. B. T. Lawton, G. A. Henderson, and E. J. Derlatka, "The Effects of Extruder Variables on the Gelatinization of Corn Starch," Canad. J. Chem. Eng., 50: 168-172 (1972).

Energy research

Research into new forms of energy is an emerging aspect of agricultural research, states Dr. [J.M.] Bell, [the University of Saskatchewan's] associate agriculture dean for research.

"Energy costs are putting enormous pressure on food and farming," he states. "We're not just talking about gasoline for trucks and tractors but also fertilizers, which are made from fossil fuel."

At the U of S, agricultural engineers are studying energy reclamation possibilities for barns. The university has built a new $3 million swine research facility that can recover excess heat produced by the animals and recycle it.

Saskatchewan's horticulture science department has developed a method of using waste heat from power plants to grow tomatoes in greenhouses. The heat is diverted from engine exhausts, the toxic gases are filtered out, and the warm air with a high concentration of carbon dioxide is pumped into greenhouses, producing large tomatoes free from disease, wind damage, or sun scald.

From University Affairs/Affaires Universitaires, June-July 1980. Copyright (c) Association of Universities and Colleges of Canada. Reprinted by permission.


Contents - Previous - Next